The present invention relates in general to an improved fusing apparatus and method, and more particularly, to a single electrode fusing apparatus and method for fusing armature wires having an electrically insulating coating, e.g., magnet wire, to the tangs of a commutator.
Fusing is a known technique for joining electrically-conductive elements in which a fusing electrode is contacted with one element adjacent the joint so that the fusing electrode forces the elements together. A ground electrode is also contacted with one of the elements, typically at a location remote from the joint, such that an electrical current is passed through the electrodes and at least one of the elements. Heat generated by the electrical current, and the high pressure applied by the fusing electrode, causes a bond to form between the elements. The fusing electrode typically has higher resistivity than the ground electrode, and ordinarily has a small contact surface region bearing on the element. Thus, the major portion of the heat used in the process ordinarily is produced in the fusing electrode itself. Fusing techniques, also referred to as "hot staking" are used in a variety of industrial applications. For example, the armature windings and commutator bars of dynamoelectric machines are typically joined to one another by fusing in mass production.
Apparatus and methods for mass production of fusing armature windings and commutator bars have been developing for many years. Initially, soft soldering or brazing was employed to join the armature wires to the commutators. However, the need for high quality motors which are reliable and economical has resulted in the growth in increased utilization of commutator fusing techniques. In addition, in order to further improve production methods, tang-type commutators were developed, as compared to the prior slotted-type commutators, which made it simpler for attaching the armature lead wires to the commutator bars by means of an extending tang. An example of such an apparatus and method which discloses efficient and rapid fusing of both the tang-type and slotted-type of commutators, is shown in Riordan et al., U.S. Pat. No. 4,224,496.
There is also known from Abe, U.S. Pat. No. 4,835,356, a three electrode spot welding apparatus designed for fusing magnet wire. The apparatus includes three electrodes, the first two of which are opposed to one another whereby a workpiece, including, for example, a magnet wire and a terminal pin to be welded together, is subjected to electric resistance welding in such a manner that the workpiece is held between the first and second electrodes. The third electrode is interposed between the first electrode and the workpiece so that one distal end face of the third electrode abuts against a workpiece engaging end of the first electrode and that the other distal end face of the third electrode is in contact with the workpiece. The proximal end of the first electrode is connected to a first terminal of a power source and the respective proximal ends of the second and third electrodes are connected to a second terminal.
The power source supplies a current to heat the third electrode and remove the plastic electrical insulation by vaporization by closing a circuit having a path through the first terminal, the first electrode, the third electrode and the second terminal during a predetermined period. After removal of the electrical insulation, the power supply supplies a current to weld the magnet wire to the workpiece by closing a circuit having a path through the first terminal, the first electrode, the third electrode, the workpiece, the second electrode and the second terminal. Although the disclosed fusing apparatus is useful in fusing magnet wire in certain applications, it is not suitable for fusing magnet wire to the tangs extending from a commutator bar as there is no access for the second electrode to the tangs.
Referring to FIG. 1 of the present case, there is shown a portion of a commutator bar 100 of a tang-type commutator as known from Riordan et al. An elongated tang 102 extends in a U-shaped configuration from the end surface of the commutator bar 100. An armature wire 104 having an electrically insulating coating, e.g., magnet wire, extends through the opening 106 of the tang 102 for fusing purposes. A fusing electrode 108 is placed on the tang 102 and a ground electrode 110 is placed on the surface of the commutator bar 100 at a remote location.
There is also shown schematically the connection between electrodes 108, 110 to a transformer 112 for controlling the current supply to the electrodes. The fusing electrode 108 is formed from a high resistance alloy such as tungsten, while the ground electrode 110 is formed from a low resistant alloy such as copper. A current path is formed between the fusing and ground electrodes 108, 110 which has a path through tang 102 and commutator bar 100. As a result of the high resistance of the fusing electrode 108, the tang 102 is heated to vaporize the electrically insulating coating on the armature wire 104 to enable subsequent fusing of the armature wire to the tang.
Although this method has enjoyed commercial success, there are a number of shortcomings and disadvantages which are desirable to overcome. For example, if the area of the brush track along the commutator bar 100 is thin, the brush track has the tendency to become annealed as a result of the application of high current between the fusing and ground electrodes 108, 110. This annealing of the commutator bar 100 within the brush track results in the material, typically copper, to become softer than normal. Subsequent to the fusing process, the surface of the commutator bars 100 are provided with a smooth surface finish and a uniform radius of curvature in what is commonly referred to as a turning process. In the event the copper material of the commutator bars 100 has become annealed, the material within the brush track of the commutator bars will have the tendency in turning to smear into and bridging the grooves formed between adjacent commutator bars resulting in the creation of electrically short circuits. This will necessitate reworking to clear the grooves to provide electrical isolation between adjacent commutator bars 100. In addition, the running of the brushes on softer material also results in greater wear to the brush track of the commutator bars 100, as well as potentially causing additional smearing of the copper material and the resulting electrical shorting.
The aforementioned fusing process although having demonstrated utility, cannot be used in the manufacture of certain commutators designed for special applications. For example, there is known an armature for use in a combustion engine fuel pump using a gasoline alcohol mixture which provides the commutator bars in the shape of individual wedges arranged in a circle within a common plane. Due to the corrosive effects of the alcohol, a corresponding wedge-shaped block of carbon material is bonded to the face of each commutator bar to provide the brush track. Although these commutators are of the tang-type, there is no suitable location for placement of the ground electrode on the commutator bars to permit use of the aforementioned fusing process as they have been covered with a block of carbon material.
Referring to FIG. 2, there is schematically shown a fusing apparatus having a pair of spaced electrodes for fusing an armature wire to the tang of a tang-type commutator which overcomes the aforementioned problems and disadvantages, and which is the subject matter of a pending application assigned to same assignee of the present application. The fusing and ground electrodes 108, 110 disclosed are arranged engaging the tang 102 in fixed spaced apart, side-by-side relationship to enable the formation of a current path between the electrodes and through a portion of the tang overlying or adjacent the armature wire 104. The current path for illustration purposes is shown by dashed lines 114. The spacing between the fusing and ground electrodes 108, 110 is such to enable the electrodes to simultaneously contact the common upper surface of the tang 102 in the manner as shown, thereby avoiding the necessity of having to engage the brush track with the ground electrode and the disadvantages resulting therefrom as previously mentioned.
It is preferred to keep the current path 114 through the tang 102 relatively short as this portion of the tang can act as a fuse link between the fusing and ground electrode 108, 110. However, the space between the fusing and ground electrodes 108, 110 results in the formation of a wedge of material from the tang 102 being extruded upwardly therebetween as the electrodes compress downwardly on the tang. The wedge has been known to interfere with the further assembly of the armature within its housing in certain applications. In addition, repeatedly contacting the tang 102 with the fusing and ground electrodes 108, 110 can cause arcing which can result in the splattering of copper from the tang onto the electrode faces thereby reducing their working life. Thus, there have been substantial unmet needs for still further improvements in an apparatus and method for fusing armature wires to tang-type commutators.